Combustion process and apparatus therefore containing separate injection of fuel and oxidant streams

ABSTRACT

A burner assembly having improved flame length and shape control is presented, which includes in exemplary emodiments at least one fuel fluid inlet and at least one oxidant fluid inlet, means for transporting the fuel fluid from the fuel inlet to a plurality of fuel outlets, the fuel fluid leaving the fuel outlets in fuel streams that are injected into a combustion chamber, means for transporting the oxidant fluid from the oxidant inlets to at least one oxidant outlet, the oxidant fluid leaving the oxidant outlets in oxidant fluid streams that are injected into the combustion chamber, with the fuel and oxidant outlets being physically separated, and geometrically arranged in order to impart to the fuel fluid streams and the oxidant fluid streams angles and velocities that allow combustion of the fuel fluid with the oxidant in a stable, wide, and luminous flame. Alternatively, injectors may be used alone or with the refractory block to inject oxidant and fuel gases. The burner assembly affords improved control over flame size and shape and may be adjusted for use with a particular furnace as required.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of assignee's patent application Ser.No. 08/668,758, filed Jun. 24, 1996, which was a continuation-in-part ofpatent application Ser. No. 08/503,336, filed Jul. 17, 1995 (abandoned).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a combustion process and an apparatustherefor containing separate injectors to introduce separately a fueland an oxidant in the combustion chamber of a furnace, so that the fuelburns with the oxidant in a wide luminous flame, and whereby thecombustion of the fuel with the oxidant generates reduced quantities ofnitrogen oxides (NO_(x)).

2. Related Art

Industrial high temperature processes, such as glass or frit melting,ferrous and non ferrous materials smelting, use large amounts of energyto transform a variety of raw materials into a hot molten product, thatis then casted, formed or otherwise disposed of in further stages of theindustrial process. This operation is generally performed in largefurnaces, that can produce as much as 500 tons per day of moltenmaterial. Combustion in the furnace of a fossil fuel, such as naturalgas, atomized fuel oil, propane, or the like, with an oxidant thatcontains oxygen is a preferred method of supplying the energy. In somecases, the combustion is supplemented by electric heating. Most of thetime, the fuel and the oxidant are introduced in the furnace throughburners, in order to generate flames. The transfer of energy from theflames to the material to be melted results from the combination ofconvection at the surface of the material, and radiation to the surfaceor into the material if it is transparent to the radiation. Flames thatare highly radiative (usually referred to as luminous flames), areusually preferred, because they provide better heat transfer and, thus,higher fuel efficiency.

For flame heating, it is also very important to have the energy from theflame evenly distributed above the surface of the material to be melted.Otherwise, hot and cold regions may co-exist in the furnace, which isnot desirable. The quality of products manufactured with material meltedin such a furnace is often poor. For example, in a bath of molten glass,there may be glass stones in cold regions, and acceleratedvolatilization of glass in hot regions. Also, broad flames are preferredbecause they yield a better bath coverage.

In many countries, particularly the United States, increasinglystringent regulations are being promulgated regarding emissions ofNO_(x). It is, therefore, important to develop combustion techniqueswherein NO_(x) formation is limited. In very high temperature processes,NO_(x) formation is promoted by long residence times of oxygen andnitrogen molecules in hot regions of the flame and the furnace. The useof substantially pure oxygen (about 90% O₂ or higher) instead of air asthe oxidant has proven to be very successful in reducing the NO_(x)emissions by as much as 90%, since all nitrogen is eliminated. However,substitution of air by substantially pure oxygen increases the flametemperature, and thus creates regions in the furnace where thereactivity of nitrogen with oxygen is high, and wherein the formation ofNO_(x) may proportionally increase, even though it is globally decreasedwhen compared to combustion with air. Also, it is impossible in practiceto eliminate all nitrogen from a furnace, because industrial furnacesare not tight to air leaks, the fuel usually contains some nitrogen, andoxygen supplied from non-cryogenic sources, such as oxygen produced by aVacuum Swing Adsorption plant (VSA), contains a small residual nitrogenconcentration.

Conventional methods of combusting fuel and oxygen for heating furnacesutilize post mix oxy-fuel burners. Conventional oxy-fuel burners have ametallic body with inlets for a fuel and an oxidant with a highconcentration of molecular oxygen, and means to transport the streamswith separate coaxially oriented channels to multiple injectors locatedat the burner tip. These burners generate high temperature flames withthe shape of a narrow pencil at the burner tip, which needs to belocated far enough into the furnace, to avoid or reduce overheating ofthe furnace walls. As a consequence of the high temperatures encounteredin melting furnaces, one important drawback of these burners is the needfor cooling, usually a jacket where a circulating fluid such as waterprovides the cooling. Such a burner is described, for example, inBritish Patent 1,215,925. Severe corrosion problems for the coolingjacket can arise particularly when the furnace atmosphere containscondensable vapors.

The gas cooled oxy-fuel burner is an improvement of the water-cooledburner. The body of the burner is protected from the furnace radiationby a refractory brick often referred to as a burner block, thatpossesses a substantially cylindrical cavity that opens into thefurnace. The burner is usually mounted at the back of the cavity, and itusually contains concentric injectors of fuel and oxidant located in thecavity, recessed from the furnace inner wall. The brick and the burnerare cooled by a peripheral annular flow of gas, usually the oxidant gas.Such burners are described e.g. in U.S. Pat. Nos. 5,346,390 and5,267,850. With this type of burner, combustion starts in the burnerblock before reaching the furnace. Thus, the flame is confined in anddirected by the cylindrical cavity as a narrow axisymmetric jet, andprovides insufficient covering of the melt in the furnace. These flameshave high peak temperatures and generate relatively large amounts ofNO_(x), because there is a direct contact between the oxygen and thefuel without dilution by the combustion products.

Another drawback of these gas cooled burners is that the flame mayoverheat and damage the furnace refractory wall because it starts in thewall itself. Also recirculation zones under the flame itself tend toaccelerate refractory wear when the furnace atmosphere chemically reactswith the refractory material of the furnace wall which may reduce thefurnace lifetime.

British Patent 1,074,826 and U.S. Pat. No. 5,299,929 disclose burnerscontaining alternated multiple oxygen and fuel injectors in parallelrows in order to obtain a flatter flame. Although this brings animprovement in terms of coverage of the melt, these burners stillproduce relatively large amounts cog of NO_(x). Another drawback ofthese burners is that they are mechanically complex to build in order toobtain a flat flame.

It is also known to inject fuel and oxidant streams by separate,distinct injectors into a combustion chamber to generate flames detachedfrom the furnace wall, with the aim of reducing refractory wear. Onesuch apparatus is described in U.S. Pat. No. 5,302,112 wherein fuel andoxidant jets are injected at a converging angle into a furnace, whichyields good mixing of the oxidant and fuel gases at the converging pointof the two jets, thus enhancing the combustion rate but shortening theflame. However, the flame of such a burner has a high peak temperatureand large quantities of nitrogen oxides are created in the furnace. Todecrease this high peak temperature and significantly reduce formationof NO_(x) it has been suggested in U.S. Pat. No. 4,378,205 to inject thefuel and/or the oxidant jets at very high velocities and to use separateinjections of fuel and oxidant gases wherein the fuel and/or the oxidantjets entrain combustion products contained in the furnace atmosphere,and are diluted before the actual combustion between the fuel and theoxidant. However, the flames generated by these burners are almostinvisible, as disclosed therein, col. 9, lines 58-65. It is, thus,extremely difficult for a furnace operator to determine and/or controlthe location of the combustion zones, and whether or not the burnerapparatus is actually turned on, which may be hazardous. Anotherdrawback of this burner is that the entrainment of combustion productspromotes strong recirculation streams of gases in the furnace, which inturn accelerates the wear of the refractory walls of the furnace. Also,the use of high velocity oxidant jets requires the use of a highpressure oxidant supply, which means that the oxidant gas needs to beeither produced or delivered at high pressure (the fuel gas is usuallyat relatively high pressure) or that the oxidant gas, such as the lowpressure oxygen gas usually supplied by a VSA unit, has to berecompressed before being injected into the furnace.

Burners in use today typically are only designed to use gaseous fuel orliquid fuels (perhaps by spray of the liquid fuel), but cannot burn bothtypes of fuel simultaneously, or switch easily from gaseous fuel toliquid fuel.

Liquid fuels present their own problems to the combustion artisan. Theliquid fuel is typically atomized, and there are several differenttechniques available for the atomization of liquid fluids. The object isto produce jets of liquid fluid droplets (also called "spray") whichhave defined geometric characteristics. The usual liquid fuels are notparticularly flammable in the liquid state: only in the gaseous stateare they able to support an oxidation reaction sufficiently rapid togive rise to the appearance of a flame. When one wishes to obtain stableflames with fuels that are liquid or viscous at ambient temperature, theprincipal difficulty is thus to "shrewdly condition" this liquid in sucha way that it evaporates rapidly in order to support oxidation reactionsin the interior of the flame.

The method currently used to achieve this "shrewd conditioning" consistsof atomizing the fuel in the form of droplets: thus, for a givenquantity of fuel, this makes possible a substantial increase in theamount of liquid surface exposed to the oxidant (the smaller the dropsare, the greater will be the interfacial surface--the site ofevaporation).

In simplified terms there are three major methods for achievingatomization of a liquid:

1. rotating cup atomization involves shredding the fluid with the air ofa moving mechanical element.

2. in mechanical atomization the fuel is compressed to very highpressures (15 to 30 bars), thus imparting to it a high kinetic energy.This energy results in shearing of the liquid when it is brought intocontact with the exterior atmosphere and thus results in the formationof droplets.

3. gaseous-fluid-assisted atomization can be used to arrive at a similarresult while achieving a saving on high pressures (2 to 6 bars).

In simplified terms one can distinguish two types ofgaseous-fluid-assisted atomization according to whether the liquid fueland atomizing fluid are brought into contact inside or outside theatomizer head. These types may be referred to as internal atomizationand external atomization.

Internal atomization is characterized by confinement of the liquid fueland atomizing fluid in an emulsion chamber. The mode of introduction ofthe two fluids into this chamber can vary considerably and has a directinfluence on the characteristics of the emulsion that exits from thechamber. Likewise, the internal geometry of this chamber (overallvolume, vanes for producing rotation, number and diameters of the inletand outlet orifices, and so forth) also affects the specificcharacteristics of the fuel/atomizing fluid mixture to be burned.

This mode of atomization generally affords an excellent quality ofatomization, that is, an emulsion composed of very small particles witha very narrow particle size distribution about these small diameters. Ata given fuel delivery rate, this emulsion quality is naturally afunction of the atomizing fluid delivery rate employed and the pressurelevel prevailing in the interior of the atomizing chamber.

For external atomization, where contact between the two phases takesplace outside of any confining enclosure, the emulsion is created mainlyby shearing of the jet of liquid fuel by the atomizing fluid. Thegeometry of the outlets for the two fluids completely determines thequality of the atomization, and particle size analysis of the dropsresulting from the contact shows a relatively wide diameter distribution(simultaneous presence of small and large particles).

In the field of liquid fuel atomization, the principal known priorityfor the invention is published European Patent Application No. 0687858A1, which claims an external atomization device that produces a verynarrow spray angle (less than 15°). This published application inparticular claims that to successfully achieve this specificcharacteristic the angle formed between the atomizing fluid and theliquid fuel must be between 5° and 30°.

Another disclosed liquid fuel atomization device is the one disclosed inEuropean Patent Application No. 0335728 A2, which claims a device forthe introduction of a fluid into a combustion enclosure through theexpedient of several distinct conduits branching from a common mainconduit.

A need exists for a burner which may operate at low pressure,particularly for the oxidant gas, while producing a wide, flat luminousflame with reduced NO_(x) emissions, and which affords a manner ofcontrolling flame length so as to adapt the flame to the furnace inwhich it is used. There also exists a need in the art for a burnerhaving the capability of burning gaseous fuels and liquid fuels, eitherat the same time or in the alternative. There is a need in thecombustion art for a liquid fuel atomizer that falls within the scope ofthe third mode of atomization, a complete device that makes possible acontrolled fluid introduction into the combustion zone that is atwo-phase mixture of atomizing gas and droplets of liquid fuel, whereinatomization takes place outside of the nozzle (external atomization) andyet permits forming distinct spray jets having high relative angles (5°to 30°). In particular the combustion art is desirous of a device foratomization of a liquid fuel using a gaseous fluid and the applicationof this device to a burner such as the burner assemblies describedherein.

SUMMARY OF THE INVENTION

In accordance with the present invention, methods and systems forcombustion of a fuel with oxygen contained in an oxidant gas arepresented, wherein the fuel and oxidant gas are injected in separatefluid streams into a combustion chamber of a high temperature furnace(having a temperature of at least, 820° C. or 1500° F.) in suchproportions that the molar ratio of oxygen in the oxidant flow to fuelflow is between about 0.95 and about 1.05 (stoichiometric ratio), thefuel and oxidant producing a wide, luminous, well-defined flame. Methodsand systems of the present invention generate reduced quantities ofNO_(x).

In general, the inventive burner assembly comprises at least one fuelfluid inlet and at least one oxidant fluid inlet, means for transportingthe fuel fluid from the fuel inlet to a plurality of fuel outlets, thefuel fluid leaving the fuel outlets in fuel streams that are injectedinto a combustion chamber, means for transporting the oxidant fluid fromthe oxidant inlets to at least one oxidant outlet, the oxidant fluidleaving the oxidant outlets in oxidant fluid streams that are injectedinto the combustion chamber, with the fuel and oxidant outlets beingphysically separated, and geometrically arranged in order to impart tothe fuel fluid streams and the oxidant fluid streams angles (referred toherein as "final" angles) and velocities (as the fuel and oxidant enterthe combustion chamber) that allow combustion of the fuel fluid with theoxidant in a stable, wide, and luminous flame.

Thus, one aspect of the invention is a burner assembly having improvedflame length and shape control, comprising:

a refractory block adapted to be in fluid connection with sources ofoxidant and fuel, the refractory block having a fuel and oxidantentrance end and a fuel and oxidant exit end, the exit end having fuelexits and oxidant exits, the refractory block further having a pluralityof fuel cavities, at least two of the fuel cavities defining a firstfuel plane, and a plurality of oxidant cavities defining a secondoxidant plane, the fuel cavities being more numerous than the oxidantcavities.

Preferred are burner assemblies of this aspect of the invention whereinthe oxidant exits are larger than the fuel exits, and embodimentswherein one or more cavities has therein an injector positioned therein,as defined herein.

Preferred refractory blocks have at least five cavities, three cavitiesat a lower portion thereof for injection of fuel into a furnacecombustion chamber, and two cavities at an upper portion thereof forinjection of an oxidant into a furnace combustion chamber.

Alternatively, especially in the case when liquid fuels such as fuel oilis used as the fuel, the oxidant cavities are preferably more numerousthan the fuel cavities.

In a particularly preferred embodiment (a so-called "bi-fuel"embodiment), the refractory block has at least one liquid fuel cavityand at least one gaseous fuel cavity. In these embodiments, it ispreferred that the liquid fuel cavity be positioned below that gaseousfuel cavities, and the gaseous fuel cavities positioned below theoxidant cavities, as further described herein.

Preferably, the fuel and oxidant exits are circular and contoured. Thecavities are preferably straight holes through the refractory block forma fluid entrance end of the block to a fluid exit end of the block. Theburner assembly of the invention may in some preferred embodimentscomprise a fuel distributor or atomizer which is a single, integralcomponent which fits inside a cavity of the refractory block, the fueldistributor having multiple fuel exits.

Another burner assembly embodiment of the invention is that comprising arefractory block having a fuel and oxidant entrance end and a fuel andoxidant exit end, and further having a single liquid fuel cavity and aplurality of oxidant cavities, the oxidant cavities defining an oxidantplane which is positioned at an upper portion of the refractory blockand above the liquid fuel cavity.

Yet another burner assembly of the invention comprises a refractoryblock having a fuel and oxidant entrance end and a fuel and oxidant exitend, and further having a plurality of fuel cavities and a plurality ofoxidant cavities, at least two of the oxidant cavities defining a firstoxidant plane which is positioned at an upper portion of the refractoryblock and above a portion of the fuel cavities defining a fuel plane,wherein at least some of the oxidant cavities form a second plane at aposition lower in the refractory block than the first oxidant plane, andwherein at least one of the oxidant cavities in the second oxidant planehas positioned therein a fuel injector having a diameter smaller thanits corresponding oxidant cavity.

Another burner assembly embodiment of the invention comprises arefractory block having a fuel and oxidant entrance end and a fuel andoxidant exit end, and further having a plurality of fuel cavities and asingle oxidant cavity, said oxidant cavity positioned at an upperportion of the refractory block and above a portion of the fuel cavitiesdefining a fuel plane. The oxidant cavity itself (cross-section) and itsexit may be non-circular, such as rectangular, oval, ellipsoidal, andthe like, in all cases preferably with contoured edges at the block exitface as described herein.

Another burner assembly of the invention comprises:

a) at least two fuel injectors defining a first plane;

b) at least one oxidant injector;

c) a wall through which the oxidant and the fuel injectors protrude intoa combustion chamber, the injectors removably secured in the wall;

wherein the oxidant injectors are positioned at a converging angletoward the first plane in the combustion chamber ranging from about 0°to about 15°.

Another aspect of the invention is a method of combustion of a fuel withan oxidant, the method comprising:

a) providing a supply of an oxidant fluid stream;

b) injecting the oxidant fluid stream into a combustion chamber tocreate at least one injected oxidant fluid stream;

c) providing a supply of a fuel fluid stream;

d) injecting the fuel fluid stream into the combustion chamber to createat least two injected fuel fluid streams;

e) creating a substantially planar sheet of fuel fluid in the combustionchamber by injecting the at least two injected fuel fluid streams intothe combustion chamber, at least two of the injected fuel fluid streamsbeing substantially located in a first fuel plane;

f) intersecting the oxidant fluid stream with the sheet of fuel fluid inthe combustion chamber; and

g) combusting the fuel fluid with the oxidant fluid in the combustionchamber.

In preferred processes in accordance with the invention, two adjacentfuel fluid streams have a final diverging angle which is not greaterthan about 15°. Other preferred methods are those wherein gaseous andliquid fuels are burned simultaneously, and methods wherein gaseous fuel(or liquid fuel) is burned first, followed by liquid fuel (or gaseousfuel).

It has been discovered that when the oxidant flow cavities are arrangedin a diverging fashion the flame is wider. In some embodiments, theflame breadth can be increased (without significant decrease in theflame length) by providing the fuel and/or oxidant flow cavities with afinal divergence angle slightly more than their initial divergenceangle, as further described herein. Also, in some preferred embodiments,oxidant and fuel injectors are used (especially for fuel) which fitinside the fuel and/or oxidant cavities.

Other embodiments of the method and apparatus of the invention includethe provision of different distances between oxidant cavities and fuelcavities, depending on the type of fuel being burned (for examplegaseous fuel vs. liquid fuel); non-parallel oxidant cavities (i.e.having diverging angles); and the provision, especially for fuel oilpurposes, of a fuel injector having multiple diverging fuelsub-injectors, the fuel injector being located in one cavity of therefractory block.

Further aspects and advantages of the invention will become apparentafter review of the following description and claims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates one embodiment of a refractory block component of aburner assembly of the present invention, wherein the fuel "sheet" ismade by using three (3) fuel injectors located in a first plane, andwherein the oxidant is supplied by two (2) injectors located in a secondplane;

FIG. 2 is a front view of the arrangement of FIG. 1;

FIG. 3 is a schematic side view of the combustion process that occurs ina furnace when the configuration of FIGS. 1 or 2 is used;

FIG. 4 is a top view of the process of FIG. 3;

FIG. 5 illustrates a second burner assembly embodiment of the presentinvention, where the fuel "sheet" is formed by using two fuel cavitiesin a first fuel plane, the oxidant being supplied by two cavities in asecond plane, and flame stabilization being supplied by an auxiliaryfuel injection in the second plane;

FIG. 6 illustrates a third burner assembly embodiment of the presentinvention, where the fuel "sheet" is formed by using two fuel cavitiesin a first fuel plane, the oxidant being supplied by two cavities in asecond plane, and wherein the flame is being stabilized by an auxiliaryoxidant cavity in the first fuel plane, between the fuel cavities.

FIG. 7 illustrates a perspective view of one burner assembly embodimentof the present invention;

FIGS. 8(a), (b) and (c) illustrate top, back and side views,respectively, of a burner assembly of the present invention includingcavities;

FIGS. 9(a) and (b) illustrate a refractory block of the presentinvention, showing various cavities;

FIGS. 10(a), (b), (c) and (d) illustrate a burner block assembly, oxygendistributor and fuel distributor of the present invention;

FIGS. 11(a), (b), (c), (d), and (e) illustrate another burner blockassembly, oxygen distributor and fuel distributor of the presentinvention;

FIGS. 12(a), (b), (c) and (d) illustrate a burner assembly of theinvention in top, side, bottom, and detail views, showing in particular,the tube sealing detail;

FIG. 13a is a perspective view of a refractory block useful in theinvention, illustrating two oxidant cavities, three fuel gas cavities,and one fuel oil cavity;

FIG. 13b is a side elevation view of the refractory block of FIG. 13b;

FIG. 13c is a side elevation view of an alternate design for therefractory block of FIG. 13a;

FIG. 14 is a side elevation view of a burner assembly without arefractory block, having only oxidant and fuel injectors;

FIG. 15 is a plan view of a refractory block, illustrating cavities;

FIG. 16 is a plan view of the refractory block of FIG. 15, illustratingan embodiment having short injectors inside the cavities;

FIG. 17 is a plan view of the refractory block of FIG. 15, illustratingan embodiment having long injectors protruding outside of the cavities;

FIG. 18 is a side elevation view of a liquid fuel atomizer useful in theinvention;

FIGS. 19a and 19b are sectional and front end elevation views,respectively, of the liquid fuel atomizer of FIG. 18;

FIG. 20a is a schematic illustration of a refractory block and cavity insame;

FIG. 20b is a schematic illustrating a preferred relationship betweenthroat diameter and gas exit diameter for an injector or cavity; and

FIGS. 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, and 33 are frontelevation views of thirteen refractory block embodiments within theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. General Aspects

According to one aspect of the present invention, the combustion processand apparatus therefor are provided which operates with low oxidantsupply pressure, such as the pressure delivered by a vacuum swingadsorption oxygen production unit. Low oxidant pressure means a pressureranging from about 105,000 to about 170,000 Pa (absolute pressure) (50 mbar to 0.7 bar/relative pressure).

According to the present invention, the fuel and the oxidant areintroduced in the furnace through separate cavities in the burnerassembly. The term "fuel", according to this invention, means, forexample, methane, natural gas, liquefied natural gas, propane, atomizedoil or the like (either in gaseous or liquid form) at either roomtemperature (about 25° C.) or in preheated form. The term "oxidant",according to the present invention, means a gas with an oxygen molarconcentration of at least 50%. Such oxidants include oxygen-enriched aircontaining at least 50% vol., oxygen such as "industrially" pure oxygen(99.5%) produced by a cryogenic air separation plant or non-pure oxygenproduced by e.g. a vacuum swing adsorption process (about 88% vol. O₂ ormore) or "impure" oxygen produced from air or any other source byfiltration, adsorption, absorption, membrane separation, or the like, ateither room temperature (about 25° C.) or in preheated form.

The cavities, as defined herein, are passages through a ceramic block orthrough a furnace wall, and preferably have a generally cylindricalcross section. Any equivalent cross section can be used, such as square,rectangular, ellipsoid, oval, and the like. Injectors are defined hereinas tubular members having an outer shape which mates with its respectivecavity, and which can be placed in its respective cavity to prolong theuse of the refractory burner block. Injectors can be either metallictubes, metallic tubes or pipes with ceramic ends, ceramic tubes, or acombination thereof. Examples of suitable ceramic materials for injectortubes include alumina, zirconia, yttria, silicon carbide, and the like.Various stainless steels may be used for the injectors if the injectorsare metallic, and metallic injectors having heat-protective refractorycoatings, employing materials such as those mentioned for ceramicinjectors, are also possible.

Injectors are preferred but not absolutely necessary. For example,injectors would not be necessary if the cavities are covered or coatedwith a layer of ceramic or any other material which withstands the hightemperature and has adequate non-porosity to avoid penetration of gasthrough the refractory block

The injectors are installed in cavities opened through the furnacewalls, or through a refractory or ceramic brick mounted in the furnacewall. In some embodiments, the length of the injector is purposely madeinsufficient to span the respective length of its cavity in the burnerblock: the fuel or oxidant flows from the injector into the cavity, thenfrom the cavity into the combustion chamber of the furnace. Thus, insome embodiments, the injector stops before any change in direction ofthe gas flow that can be imparted by the geometry of the cavity; inother embodiments, the injector may protrude out of the refractory blockand into the combustion chamber. In other embodiments there may be noinjectors at all.

The fuel injection is preferably made by at least two, preferablyidentical, cavities which axis are located preferably in a same plane,further referred to as the first fuel plane. The fuel and oxidantoutlets are physically separated and geometrically arranged in order toimpart to the fuel fluid streams and the oxidant fluid streams anglesand velocities that allow combustion of the fuel fluid with the oxidantin a stable, wide, and luminous flame.

In preferred embodiments, the fuel cavities diverge at an initial angle,and then this initial divergence angle increases slightly just beforethe fuel enters the combustion chamber to the final divergence angle.This final divergence angle is preferably only a few degrees larger thanthe first divergence angle. A preferred final angle between two adjacentfuel cavities is between about 3 and 10 degrees. The distance l betweenthe extremities of the cavities when the fuel enters the combustionchamber of the furnace is comprised preferably between about 4 and 10times the inner diameter d of each fuel injector in the first plane. Thefirst plane is preferably but not necessarily parallel to the meltsurface. When the fuel injector or cavity is not circular, the dimension"d" is an equivalent diameter corresponding to the cross-sectional areaof an equalivalent circular injector or cavity. The combination of thefuel jets from the fuel cavities is such that it creates a fuel "sheet".By fuel "sheet", it is meant a substantially continuous cloud of fueldroplets (if liquid) or fuel gas in an angle of the first plane of atmost about 120°, preferably between about 20° and 60°, and preferablyabout symmetrical relative to the longitudinal axis of symmetry of thefuel cavities. The velocity of the fuel gas in the cavities ispreferably at least about 15 m/s.

According to one preferred embodiment of the present invention, aprocess is provided wherein a "sheet" of fuel fluid is generated abovethe surface to be heated, e.g. by means of at least two fuel cavitiesthat make a final diverging angle preferably smaller than about 15degrees, said fuel cavities being located in a first plane, an oxidantfluid having a lower velocity than that of the fuel fluid (preferablynot exceeding about 60 meters per second (m/s)) being injected above thesurface to be heated, preferably with at least two oxygen cavities, twoadjacent oxygen cavities making a final diverging angle smaller thanabout 15 degrees. These cavities are preferably located in a secondplane, which converges to and intersects with the first plane in thecombustion chamber. The low velocity oxidant fluid jets which intersectwith the fuel sheet, are dragged by the fuel flow along the fuel sheet,and create a combustion zone that stretches along the "sheet".Accordingly, at the beginning of the combustion zone of the combustionchamber, a fuel-rich region is maintained at the underside of the fuelcloud where significant amounts of soot are formed. The soot and thefuel are then progressively oxidized by the oxidant that diffuses alongthe combustion zone.

According to a particular embodiment of the invention, a method ofcombustion in a combustion zone is provided for a burner assemblycontaining at least two fuel fluid cavities, at least one oxidant fluidcavity and at least one exit face at which the fuel fluid cavities andoxidant fluid cavity terminates, the process entailing:

providing a supply of an oxidant fluid stream;

injecting said oxidant fluid stream through said at least one oxidantfluid cavity to create at least one injected oxidant fluid stream;

providing a supply of a fuel fluid stream;

injecting said fuel fluid stream through said at least two fuel fluidcavities to create at least two injected fuel fluid streams;

creating a substantially planar sheet of fuel fluid by injecting the atleast two injected fuel fluid streams with a final diverging angle, atleast two injected fuel fluid streams being substantially located in afirst fuel plane;

intersecting the oxidant fluid stream with the sheet of fuel fluid inthe combustion zone; and

combusting the oxidant fluid with the fuel fluid in the combustion zone.

Additionally, the invention also provides stabilization of the flamewith an auxiliary injection of fuel and/or oxidant gases.

According to another embodiment of the invention, it is possible to alsohave additional fuel cavities, e.g. located in a second fuel plane,beneath the first fuel plane and preferably parallel to or slightlyconverging with the first fuel plane.

The injection of the oxidant fluid is made by at least two, preferablyidentical, cavities whose axis are located in the same plane, namely afirst oxidant plane. The axial distance L between the tips of theoxidant cavities where the oxidant flow enters the combustion chamber ofthe furnace is comprised preferably between about 2 and about 10 timesthe inner diameter D (or equivalent diameter, as defined previously for"d") of each oxidant injector in the second plane. Two adjacent oxidantcavities make a final diverging angle (in the direction of the flow)between about 0 and 15 degrees, preferably between about 0 and 7degrees. The oxidant velocity in the cavities is smaller than the fuelvelocity in the cavities of the first oxidant plane, and preferablysmaller than about 60 meters per second (m/s). In some embodiments ofthe invention, the oxidant cavities contain so-called swirlers, intendedto give to the oxidant streams a swirling motion to increase thespreading of the oxidant streams in the combustion zone, and improve themixing between the oxidant and the fuel sheet. Suitable swirlers aremetallic fins or twisted stripes of metal placed in the cavities orinjectors.

The total quantities of fuel and oxidant used by the combustion systemare such that the flow of oxygen ranges from about 0.95 to about 1.05 ofthe theoretical stoichiometric flow of oxygen necessary to obtain thecomplete combustion of the fuel flow. Another expression of thisstatement is that the combustion ratio is between 0.95 and 1.05.

The angle α between the first fuel plane and the second (oxidant) planeis between about 0 and 20 degrees, the first fuel plane and second planeconverging toward the combustion chamber. The distance h between thefirst fuel plane and the second plane is at least equal to 2 times thediameter D, in the vertical plane at the exit of the cavities, with thefirst fuel plane being considered as substantially horizontal.

The present invention also relates to a burner assembly comprising atleast two fuel fluid cavities, at least one oxidant fluid cavity and atleast one exit face at which the fuel fluid cavities and the oxidantfluid cavity terminates, comprising:

means for supplying an oxidant fluid stream;

means to inject said oxidant fluid stream in said at least one oxidantfluid cavity to create at least one injected oxidant fluid stream;

means for supplying a fuel fluid stream;

means to inject said fuel fluid stream in said at least two fuel fluidcavities to create at least two injected fuel fluid streams;

wherein the directions of injection of the oxidant fluid stream and thefuel fluid stream are substantially converging while the directions ofat least two adjacent fuel fluid channels are diverging.

A first refractory block component 5 of a burner assembly embodiment ofthe invention is illustrated in FIG. 1, having three fuel fluid cavities1a, 1b, and 1c in a first plane 2, and two oxidant fluid cavities 3a and3b in the second plane 4. The two first and second planes (2 and 4) makean angle α. The three fuel fluid cavities 1a, 1b, and 1c make an angle βbetween two adjacent ones, preferably the same. Preferably, the axis ofthe middle fuel cavity 1b is perpendicular to an exit face 10 ofrefractory block 5.

FIG. 2 illustrates a front view of block 5 of FIG. 1. On FIG. 2, drepresents the diameter of fuel cavities 1a, 1b, and 1c at exit face 10;l represents their respective axial separation distance at exit face 10;D represents the diameter of oxidant cavities 3a and 3b at exit face 10;and L their respective axial separation distance at exit face 10. "h"represents the distance between planes 2 and 4 at exit face 10 of block5. It is to be recognized that all dimensions described herein withreference to FIG. 2 may be modified based on the particular fuel used.For example, if fuel oil is used, the distance h would tend to begreater than if natural gas were used as the fuel.

FIG. 3 represents a schematic side elevation view of the operation ofthe combustion system of FIGS. 1 and 2 as used in, for example, a glassmelting tank 12, while FIG. 4 illustrates a perspective view of thesystem of FIGS. 1-3. A fuel "sheet" or "cloud" is formed by fuel fluidstreams exiting the fuel cavities in the first plane 2. Jets of oxidant6 exit the cavities of the second plane 4, and intersect the fuel sheetin the combustion chamber 70 of the furnace. Combustion of the fuel withthe oxidant occurs at an interface between the two flows to generate aflame 8 above the melt 9. In the early stages of the combustion process,the region located under the flame is fuel rich, which promotes theformation of carbon particles (soot) and thus enhances the luminosity ofthe flame. This is one of the characteristics of the invention: byspreading the fuel in a plane and creating planar layer or a "sheet" allover the melt substantially parallel to the melt and directing oxygenfrom above into the direction of the "sheet" to intersect the "sheet",then combustion preferably occurs in between the oxidant fluid and thefuel fluid where they cross each other. Before the intersection of theplanes, the flow is stratified, the bottom portion of the flame (whichis closer to the melt) being fuel rich and thus generating soot becauseof the excess amount of fuel which is cracked by the high temperatureflame. This soot is entrained by the gaseous stream beyond theintersection of the planes, to be further reburned in the flame which isthus more luminous.

The configuration illustrated in FIGS. 1 to 3 was tested in a pilotscale furnace of square cross section (1 m wide and 2.5 meters long).The furnace was heated up to 820° C. (1500° F.) by an assist oxygennatural gas burner. When the furnace temperature was high enough, thecombustion system of the invention was started and the assist burnershut down. The flame was viewed from the side of the furnace which hadviewing ports. When necessary, the burner assembly including therefractory block illustrated in FIG. 1 was rotated (e.g. by 90 degrees),so that the flame could be better monitored from the side viewports. Inall experiments, the first plane of the natural gas cavities wasparallel to one of the furnace walls (side or bottom).

The combustion system that was tested used natural gas flowing at about32 nm³ /hr (1200 scfh) as a fuel fluid and pure oxygen flowing at about64 nm³ /hr (2400 scfh) as the oxidant fluid under a pressure of about100 m bar above the furnace pressure. This represents a combustion ratioof about 1. The distance L between the oxygen cavities was 15 cm. Theangle between the natural gas cavities was 5 degrees. The arrangementallowed to vary the distance h between the first plane and the secondplane from 2.5 cm to 10 cm, and the relative angle of the two oxygencavities from 0 to 5 degrees. The cavities included injectors made ofceramic mullite tubes (stainless steel tubes have been further testedtoo). All cavities were mounted in cavities drilled through refractorymaterial (referred to as the refractory block 5). The diameter of thenatural gas cavities was varied between 0.925 cm and 1.58 cm (0.364inches and 0.622 inches) so that fuel fluid velocities of 44 m/s, 26m/s, and 16 m/s, were respectively achieved. The diameter of the oxygencavities was varied between 1.9 and 2.66 cm (0.75 and 1.049 inches) sothat oxygen velocities of 16 m/s, 27 m/s, and 31 m/s were achieved. TheCO, O₂, CO₂, NO_(x) contents in the flue gases were continuouslymonitored. Similar conditions with excess oxygen and furnace leaking(air ingress) were maintained during all the tests so that the NO_(x)emissions from the various configurations can be compared. The averagefurnace temperature was about 1450° C. for all the tests. A samplingprobe was also introduced in the furnace, at a distance of two metersfrom the block 5 to measure the local CO concentration in the flame. Lowmeasured CO concentrations at the sampling probe indicate short flames.Another indication of short flames for this particular furnace is theobservation of relatively low temperature flue gases, with about thesame stoichiometric conditions.

Also tested in the pilot furnace was an oxygen-natural gas burner of thepost mix type, with a generic "tube in tube" design: injection ofnatural gas surrounded by an annular oxygen stream. This burner was usedas a reference. The burner was attached to the furnace wall, andgenerated 500 ppm of NO_(x) in the flue gases.

For the system according to the invention, when the distance h was equalto 2.5. cm and the angle between the two planes was equal to 0 degree, astable flame was generated, detached from the burner block. There wasevidence of very good mixing between the fuel and oxygen jets. The flamelength was short (1.5 m), especially when the velocity of the fuel was 2to 4 times the velocity of the oxygen. The NO_(x) concentration wasabout 400 ppm. The flame appeared to be slightly broader than thereference flame.

As the distance h was increased (still maintaining α=0°), the mixingbetween natural gas and oxygen was delayed, and some soot was formed inthe flame. At h=8 cm, the flame appeared very voluminous and very long.Large amounts of soot were observed on the water cooled sampling probeat 2 meters from the burner block in which the burner is installed. Theflame was visible, but its boundaries were hard to define because theflame was unstable. The furnace pressure exhibited important pressurefluctuations due to this instability. The NO_(x) emissions weredramatically reduced to about 60 ppm. Although the quality of thecombustion seemed relatively poor, there was no CO left in the fluegases.

At h=8 cm, an improvement of the flame stability was obtained when theangle between the first and the second planes was increased to 5°, 10°,and 20°. The angle α=20° gave the best stability. Increasing a beyond20° did not significantly reduce the amount of soot formed and the flameluminosity, did not reduce the flame width, but increased the NO_(x)concentration in the flue gases, and decreased the flame length. Alsothe impingement of the oxygen jets on the fuel sheet at the angle of20°, even when the oxygen velocity was reduced, modified the shape ofthe "sheet", and deflected it towards the wall parallel to the firstplane, which was found to be undesirable. The flame could be consideredas being stable or very stable (for h=8 cm) for an angle comprisedbetween about 5° and 15°.

In a given configuration, increasing the ratio of natural gas velocityto oxygen velocity improved the flame stability. For example theconfiguration where α=10° and h=8 cm is stable when the fuel velocity is70 m/s and the oxygen velocity is 16 m/s. However, the stability effectis detrimental to the flame length and luminosity. The larger naturalgas velocity was obtained by closing the natural gas injector located inthe center of the first plane, so that all the natural gas was flowingthrough the two outer natural gas cavities.

It has been unexpectedly found, however, that the flame stability couldbe significantly improved without affecting the flame luminosity and theflame length if one natural gas injector is located in between the twooxygen cavities of the second plane, such as indicated on FIG. 5,preferably if one of the natural gas injector 21 in the first plane 2 ismoved to the second plane 4, or close to it, substantially at the samedistance from each oxygen injector 23, 24. The other two fuel cavities20, 22 keep the same position. Most preferably, if three gas cavities20, 21, 22 and two oxygen cavities 23, 24 are provided, it is preferredto have two natural gas cavities 20, 22 in the first plane 2, two oxygencavities 23, 24 in the second plane 4 and a third natural gas injector21 located close to or in the second plane 4, preferably atsubstantially the same distance from the fuel cavities, said distancebeing preferably smaller than or preferably at most equal in thedistance from the two oxygen cavities. Approximately one third of thenatural gas flow may be diverted from the first plane 2 to improve theflame stability. A stabilizing combustion zone is created between thefirst fuel plane 2 and the second (oxidant) plane 4, that initiates thecombustion above the main fuel sheet. A preferred location for thestabilizing natural auxiliary jet is the median plane between the oxygencavities. In conditions where the natural gas velocity was 44 m/s, theoxygen velocity was 16 m/s, the distance h was 8 cm, and the angle α was10°, lower NO_(x) emissions (63 ppm) were found when the auxiliarynatural gas injector was located exactly in between the oxygen cavities,than when the auxiliary natural gas injector was closer to one or theother oxygen cavities (74 ppm). However, in both cases, NO_(x) emissionswere low.

Modifying the angle α can be advantageously used to increase the heattransfer to the wall towards the first plane. It has been found thatincreasing the angle α from 0° to 10° increased the temperaturedifference between the wall located near the first plane 2 and theopposed wall from 0° C. to 27° C. At α=20° the temperature differencewas about 32° C.

A combustion system according to the invention can thus be used toincrease the heat transfer toward the load and reduce the furnace crowntemperature.

According to another embodiment of the invention, an equivalentimprovement of the flame stability can be obtained if an auxiliaryoxygen injector 25 is installed in the first plane 2 of the fuelcavities 20, 22, as shown for example on FIG. 6. (The same relativelocations of this oxygen injector and the gas cavities applies, asdisclosed on FIG. 5.) In this configuration, there are two oxygencavities 23, 24 in the second plane 4 and two fuel cavities 20, 22 andone oxygen injector 25 in the first fuel plane 2.

As it appears from the above description of the operation of thecombustion system, the flame length can be varied by changing the anglea between the second plane 4 of the oxygen cavities and the first fuelplane 2 of the fuel cavities. The flame stability is enhanced andmaintained over the range of flame length adjustment by an auxiliaryinjection of fuel near the oxygen cavities, or an auxiliary injection ofoxygen near the fuel cavities. Changing the angle between the two flamescan also be used to increase the heat transfer towards the load of thefurnace, and thus improve the efficiency of the fuel burnt. In the caseof glass furnaces, additional heat transfer in some areas of furnacescan be useful to enhance the convective circulations of the molten glassand/or increase the residence time of the molten glass in the furnace,which improves the glass quality.

Combustion systems of the present invention are intended to be used, forexample, to replace air-fuel combustion systems in already existingfurnaces, and/or to be used as the main source of energy in newfurnaces.

In accordance with yet another aspect of the present invention, a burneris provided having oxidant exits which are slightly angled to the sides,and generally contoured, preferably rounded, at their tips (i.e. at theexit face 10). Quite surprisingly, it has been discovered that theangled exits allow the oxygen flow and, thus, the flame to be wider andprevent fuel from exiting unburned. Additionally, the rounded tips causeless turbulence, and, hence, afford a greater control over flame shape.

In fact, obtainment of a particular flame shape is most important and itis quite advantageous to be able to adjust flame shape to customer need.

These and other aspects of the present invention will be now be furtherdescribed by reference to FIGS. 7-12.

The principal components of a preferred burner assembly depicted in FIG.7 are: 1) a refractory block 5; 2) a mounting bracket assembly 72; 3) afuel distributor 74, located at the bottom of the mounting bracketassembly, and 4) an oxidant distributor 76, located at the top of themounting bracket assembly. Fuel is supplied through an inlet 78. Oxidantis supplied to the burner assembly through an inlet 80.

In FIGS. 8a (plan view), 8b (end elevation) and 8c (side elevation) thefuel and oxidant cavities are straight holes through refractory block 5.The gas exit of each oxidant cavity and each fuel cavity have roundededges at the gas exit face 10 as opposed to straight edges. The roundededges reduce the velocity gradient between the gas flows ejected fromthe block and the surrounding atmosphere, which prevents particulates orvolatile species contained in the atmosphere to build-up around theoutlets of the cavities which in turn would alter the geometry of thecavities. This is particularly important in the case of the natural gascavities, because the build-up process can be aggravated by the thermalcracking of the natural gas and the formation of coke deposits at thenatural gas exits from the refractory blocks, which can alter flowdirection in the furnace.

The bottom cavities used for the fuel make a diverging angle β in orderto distribute the fuel gas flow in a sheet pattern. An angle β of 5degrees is represented in FIG. 8(a). From results of numericalsimulations, it was found that the flame width could be increased byincreasing the angle of the natural gas cavities. For instance, β=7.5degrees produce a wider flame compared to β=5 degrees, withoutsignificantly reducing the flame length.

The refractory block 5 illustrated in FIGS. 9a (side elevation) and 9b(plan view) has five cavities: three cavities at the bottom for theinjection of fuel in the furnace, and two cavities at the top for theoxidant injection. The refractory block 5 depicted in FIGS. 9a and 9b ispreferably a single piece of refractory material having multiplecavities or through holes therethrough, such as cavities 91 and 92 foroxidant, and cavities 94, 96, and 98 for fuel. In the embodimentillustrated in FIGS. 9a and 9b, note that oxidant cavities 91 and 92 areinitially parallel to each other and with the fuel cavities (seeportions 91a and 92a), but then angle away from each other at an angleof 2Θ, and toward the fuel cavities at an angle μ. Also note that fuelcavities 94 and 98 (the two on either side of the block 5) angle awayfrom the central fuel cavity 96 at an angle, preferably also Θ. Thisdesign allows the ability to position the exits of the fuel cavitiescloser to one another than in the embodiment illustrated in FIG. 8.Closer fuel exits might be useful when the fuel is fuel oil.

Suitable materials for the refractory block are fused zirconia (ZrO₂),fused cast AZS (alumina-zirconia-silica) rebonded AZS, or fused castalumina (Al₂ O₃). The choice of a particular material is dictated amongother parameters by the type of glass melted in the glass tank.

Straight cavities as illustrated in FIG. 8 are easy to clean in casesome material happens to block the gas outlets. However, angling out thelast few centimeters of the cavities is enough to impart a divergingangle to the fuel gas streams. Such a cavity design is illustrated inFIGS. 10a (plan view illustrating oxidant cavities only), 10b (plan viewillustrating fuel and oxidant cavities), 10c (back end elevation) and10d (side elevation), in the case of the oxidant cavities. Each of theoxidant cavities 91 and 92 comprise two straight flow paths 91a and 92a,initially parallel, that make a small outward angle near the exit (flowpaths). The purpose of the small angle is to direct the flow of oxidantoutwards, in a similar fashion as the jets of fuel gas. In laboratoryand field tests, angling out the oxidant (in the tests oxygen was used)cavities proved to give more stability to the flame and is beneficial tothe burner operation by widening flame width without significantlydecreasing flame length. A preferred configuration is when the anglebetween the two oxidant cavities at their exits is equal to the anglebetween the two side fuel gas cavities.

The embodiment illustrated in FIGS. 11a-e is similar to the embodimentillustrated in FIG. 10, except that FIG. 11e illustrates that the twoside fuel injectors make a small angle outward near their exit; thusboth of the oxidant cavities 91b and 92b veer outward near exit face 10,as well as the two side fuel injectors 94b and 98b.

From FIGS. 8, 10, and 11 it can be seen that the oxygen cavities arepreferably angled downward toward the natural gas cavities. The angleshown on the drawings is 10 degrees. Under certain conditions, a smallerangle (such as 7.5 degrees) can be used. Again angling out the last fewinches of the cavities is enough to impart a converging angle betweenthe oxygen jets and the natural jets.

The burner assembly illustrated in FIG. 12 includes a mounting bracketmade of two parts that are positioned on each of the upper and lowerportions of refractory block 5, fastened together by bolts 32 screwed inplate P. The mounting bracket assembly slides in vertical grooves G₁ andG₂ in the refractory block, and is thus well anchored to the block oncethe bolts 60 and 61 are in place.

An oxidant distributor 30 of FIG. 12 is mounted directly on the mountingbracket assembly with bolts 32 and plate 34. Tightness between thedistributor and the block is insured by a gasket 36. The distributorcomprises a plate 38 on which oxidant injectors 40 and 41 are welded.When mounted on the burner, the oxidant injectors penetrate intocavities in burner block 5, and stop about 10 cm (4 inches) away fromexit face 10 of the block, before any change in direction of the flowthat can be imparted by the geometry of the oxidant cavities.

A fuel gas distributor 50 is mounted on a plate 52 with quick connectclamps 53a and 53b. Plate 52 is attached to the mounting bracket bybolts 54a and 54b. Tightness between plate 52 and refractory block 5 isinsured by a gasket 56. Three gas injectors 58a, 58b, and 58c penetrateinto refractory block 5, and stop about 10 cm (4 inches) away from exitface 10 of block 5 before any change in direction of the flow that canbe imparted by the geometry of the fuel gas cavities. The inlet heads ofthe fuel gas injectors are imprisoned between the injector 60 and plate52. Fuel gas injector tightness is insured by O-rings 62 and 64positioned on the inlet head of the fuel gas injectors. The tube sealingdetail in FIG. 12(d) is noted, in particular.

FIG. 13a is a perspective view of a refractory block 5 useful in theinvention, illustrating the exits of two oxidant cavities 91a and 91b,the exits of three fuel gas cavities 94a, 94b, and 94c, and the exit ofone liquid fuel cavity 95. FIG. 13b is a gas exit end elevation view ofthe refractory block of FIG. 13b, illustrating distances d₁ and d₂,wherein d₂ is the distance between a plane containing the axial centerof the two oxidant cavities 91 (second plane) and the liquid fuel cavity95, and d₁ is the distance between the second plane and a planecontaining the three fuel gas cavities 94. (Note that d₁ is the samedistance as h in FIG. 2) FIG. 13c is a gas exit end elevation view of analternate design for the refractory block of FIG. 13a, illustrating anembodiment wherein there are in fact no gaseous fuel exits, and only oneliquid fuel exit 97 is present (the two oxidant gas exits are the sameas in FIG. 13a).

A relationship has been found to exist between the power of theinventive burner and the distances d₁ =h, d₂, d, D, L, and 21 asdepicted in FIGS. 2, 13b, and 22. If the distance between oxygen andnatural gas exits from the burner is defined by d₁, then

    d.sub.1 =A(P/1000).sup.1/2

wherein P is the burner capacity in kilowatts (kW), and about 500mm<A<about 150 mm. The preferred value for A is about 110 mm. If d₂ isdefined as the distance from the plane containing the fuel gas exits tothe parallel plane containing the liquid fuel exit, then

    d.sub.2 =d.sub.1 ρ.sub.FO /ρ.sub.NG  (I.sub.FO +I.sub.AIR /I.sub.NG !(10.sup.-3)

wherein:

I_(FO) =liquid fuel momentum in the cavity or injector,

I_(AIR) =atomizing air momentum in the injector or cavity,

I_(NG) =gaseous fuel momentum,

ρ_(FO) =liquid fuel specific gravity, and

ρ_(NG) =gaseous fuel specific gravity.

For the preferred value of A and for the following momentum values:

I_(FO) =0.06N,

I_(AIR) =1.79N,

I_(NG) =1.56N,

ρ_(FO) =0.9 kg/dm³, and

ρ_(NG) =0.74 kg/m³,

the dimensional values listed in Table 1 are available.

                  TABLE 1                                                         ______________________________________                                        Burner Power                                                                  Power                                                                         (kW)  500    1000   1500 2000 3000 4000 5000 6000 7000                        ______________________________________                                        d.sub.1                                                                             78     110    135  156  191  220  246  270  291                         (mm)                                                                          d.sub.2                                                                             113    160    196  227  278  320  358  392  423                         (mm)                                                                          d     10.6   15     18.4 21.2 26   30   33.5 36.7 39.7                        (mm)                                                                          D     29.7   42     51.4 59.4 72.7 84   93.9 102.9                                                                              111.1                       (mm)                                                                          L     113.1  160    196  226.3                                                                              277.1                                                                              320  357.8                                                                              391.9                                                                              423.3                       (mm)                                                                          2l    99     140    171.5                                                                              198  242.5                                                                              280  313  342.9                                                                              370.4                       (mm)                                                                          ______________________________________                                    

FIG. 14 is a side elevation view of a burner assembly without arefractory block, having only oxidant injectors 102 and fuel injectors104 inserted through and secured in a wall 100 of a furnace or glassmelt tank, in accordance with another burner assembly embodiment of thepresent invention. The oxidant injectors are illustrated as beingstraight, with no change in angle, but of course the injectors mayinitially be parallel with the fuel injectors, and then changedirection, so that the fuel and oxidant mix in the combustion chamber.This embodiment may also be used when the fuel is a liquid fuel. Thisarrangement, as well as the embodiment illustrated in FIG. 17, may beuseful in that the fuel and oxidant may be preheated by combusted fuelin the combustion chamber, adding to the efficiency of fuel combustion.

FIG. 15 is a plan view of a refractory block, illustrating cavities(oxidant or fuel) 91a and 91b; FIG. 16 is a plan view of the refractoryblock of FIG. 15, illustrating an embodiment having short injectors 102aand 102b inside the cavities; and FIG. 17 is a plan view of therefractory block of FIG. 15, illustrating an embodiment having longinjectors 102a and 102b protruding outside of the cavities.

II. Specifics for Liquid Fuel Atomization

FIG. 18 is a sectional view of a liquid fuel atomizer 200 useful in theinvention.

As stated previously in the Background section, the present aspect ofthe invention falls within the scope of the third mode of liquid fuelatomization; it describes a complete device that makes possible controlof the atomization of a liquid fuel using a gaseous fluid and theapplication of this device to a burner, such as the inventive burnerassemblies described herein.

In the present invention, even though the geometry for fluidintroduction seems similar, the fluid introduction into the combustionzone is a two-phase mixture of atomizing gas and droplets of liquidfuel. Further, the specific characteristics of the invention reside inthe fact that atomization takes place outside of the nozzle (externalatomization) and yet permits forming distinct spray jets having highrelative angles (5° to 30°).

The fundamental constraint on a liquid fuel atomizer operating in hightemperature combustion zones (varying from 1400° C. to 1700° C.) is itsdurability. Moreover, the flame produced at the outlet of this injectoris an oxy flame residing at an even higher temperature (>2200° C.).These high temperatures must not under any circumstance lead to anydamage of the components comprising this device. This device must beable to function continuously under these conditions and with aninspection frequency on the order of months.

The inventive liquid fuel atomizer is capable of ensuring the productionof a single broad flame, a single long flame, or several short flamessimultaneously.

The atomization principle adopted in the atomizer of the presentinvention is external atomization. This choice was essentially imposedby the constraints of thermal resistance and maintenance of the injectorwhen used in a third generation burner (self-cooled burner with separateinjection). In effect, the temperature levels potentially reached by thefuel injectors in burners of this type are very much higher than thosepreviously encountered with first and second generation burners.

These temperature levels therefore do not allow direct contact betweenthe fuel spray and high temperature metal parts. This contact wouldinevitably lead to coke formation at the tip of the injector and, inshort order, plugging of the tip.

External atomization is the only mode of atomization which is able toobviate this difficulty and thereby ensure an injector servicingfrequency on the order of a month. In effect, this atomization ischaracterized by the formation of the spray outside of the injector,thus precluding all contact between the spray and metal parts.

Moreover, as we will see in the description of the device, the liquidfuel is constantly "sheathed" by the atomizing fluid, which, beingheated preferentially, draws off the heat flux transmitted to theinjector. By playing the role of a heat transfer fluid for cooling, theatomizing fluid thus protects the liquid fuel from any excessive heatingthat could produce the beginnings of coke formation.

A. Description of the Inventive Liquid Atomization Device (FIG. 18)

The liquid fuel atomizer of the present invention comprises:

a liquid fuel injector, and

an outer nozzle completely surrounding the injector.

To facilitate cleaning of the atomization device, this outer nozzle iscomposed of two symmetrical cowls which, when they are positioned faceto face, form channels for flow of atomization fluid, as furtherexplained in part IIB.

Reference will now be made to FIGS. 18-19. In FIG. 18, the liquid fuelatomizer 200 is composed of a first hollow cylinder 202 having aninternal surface 204 of inside diameter D_(OI), and an outside surface206 having outside diameter D_(OE). Hollow cylinder 202 has a fuel exitend 203 having a single fuel exit fluidly connected to a plurality ofhollow elementary conduits C₁, C₂, and C₃. Liquid fuel is delivered intofirst hollow cylinder 202 having diameter D_(OI) and then to theinterior of all the hollow elementary conduits to emerge from anatomized fuel exit end 208 of the liquid fuel atomizer 200 (combustionchamber side). The number of hollow elementary conduits C can range from2 to 5 (typically 2 or 3). The axes of all the hollow elementaryconduits C are in the same plane ("spray plane"); this plane containsthe axis of the first hollow cylinder 202.

In FIG. 18 and the accompanying discussion, the symbols which carry anumeral in superior position will refer to the number of elementaryatomizer.

Each of the hollow elementary conduits C will have an inside diameterD^(i) ₁ (into which the liquid fuel will flow) and an outside "diameter"D^(i) ₂. The external shape of the hollow elementary conduits C is notnecessarily cylindrical: it can be parallelepipedal with square section.In such a case, D^(i) ₂ is the side of the square, the side parallel tothe "spray plane."

Each of these hollow elementary conduits C has an inclination angleα^(i) ₁, with respect to the axis of the cylinder (D_(OI) ; D_(OE));this angle is in the "spray plane."

The length of each of these hollow elementary conduits C (distancebetween the first hollow cylinder 202 and the end of the hollowelementary conduit) is L^(i) ₁.

B. Description of the Outer Nozzle (FIGS. 19a and 19b)

The outer nozzle 210 is formed of a second hollow cylinder 212 (havingan inside surface 214 of diameter D_(FI), and an external surface 216 ofoutside diameter D_(FE)) which is extended by a profiled part 218comprised of two symmetrical cowls 219 and 221. The interior of profiledpart 218 of nozzle 210 is pierced by channels 220, 222, 224 which mergewith the second hollow cylinder 212. The number of channels 220, 222,224 is equal to the number of hollow elementary conduits C present inouter nozzle 210. All the axes of these channels 220, 222, 224 arelocated in the "spray plane", denoted by solid line eff which alsocontains the axis of second hollow cylinder 212. Solid line e_(ff)denotes the separation between symmetrical cowls 219 and 221.

The channels 220, 222, 224 have a length L^(i) ₂ and a diameter D^(i) ₃.The shape of the channels is the same as that of the elementary conduitsof the fuel injector: it can be cylindrical or parallelepipedal withsquare section (in the former case, D^(i) ₃ is the diameter of thecylinder; in the latter case D^(i) ₃ is the length of the side of thesquare, the side parallel to the "spray plane").

Each of channels 220, 222, 224 has an inclination angle α^(i) ₂ withrespect to the axis of the second hollow cylinder 212; this angle is inthe "spray plane."

The axis of first hollow cylinder 202 coincides with that of secondhollow cylinder 212.

The atomizing fluid is delivered through second hollow cylinder 212,between surfaces 206 and 214, and then to the interior of the outernozzle 210 and through channels 220, 222, and 224, and to exit end 208.

C. Details of an "Elementary Atomizer" (FIG. 18)

An elementary atomizer is comprised of

a hollow elementary conduit C₃ inside which the liquid fuel flows. Theoutside surface 226 of a hollow elementary conduit C₃ can be cylindricalor parallelepipedal with square section; the internal geometry of thehollow elementary conduit C₃ is cylindrical.

a machined channel 224 in which hollow elementary conduit C₃ isarranged. The geometry of this channel 224 is the same as the externalgeometry of hollow elementary conduit C₃. The atomizing fluid circulatesin channel 224, around hollow elementary conduit C₃.

To provide external atomization of the liquid fuel by the atomizingfluid, all the elementary atomizers composing the atomization device 200of the invention conform to precise technical criteria.

For each elementary atomizer i, where i can be equal to 1, 2, 3, 4, or 5according to the number of elementary atomizers which the atomizationdevice of the invention has, the following apply:

1. To avoid any plugging of the hollow elementary conduit C where theliquid fuel circulates:

    D.sup.i.sub.1 ≧0.5 mm and typically D.sup.i.sub.1 =2 mm.

2. The thickness of the hollow elementary conduit C must be as small aspossible in order to permit immediate shearing of the jet of liquid fuelas it exits from the hollow elementary conduit C by the atomizing fluidwhich flows along its periphery: the smaller the thickness of materialseparating the fuel from the atomizing fluid is, the more rapidly thetwo fluids will be brought in contact and thus the more effective theshearing between the two jets will be. Furthermore, a reduction in thethickness of the conduit also favors the formation of a spray having alow solid angle.

3. Lastly, a decrease in this thickness also serves to decrease theamount of material subjected to the thermal radiation from thecombustion chamber: the smaller the thickness of the conduit is, themore limited the amount of heat captured by the conduit will be. Thetemperature of the conduit will be lowered as a consequence.

On the other hand, this thickness must be sufficient to providemechanical resistance to the shocks that occur during manipulation ofthe atomization device.

    D.sup.i.sub.2 -D.sup.i.sub.1 ≦6 mm, and typically and preferably

    D.sup.i.sub.2 -D.sup.i.sub.1 =1 mm.

The space between the outside surface 226 of the hollow elementaryconduit C₃ and the inside of the channel 224 ("the flame") must beproportioned in such a way that the velocity of the atomizing fluid(V_(atomizing) fluid) follows the relationship:

    Mach 0.3≦V.sub.atomizing fluid ≦Mach 1.2.

Accordingly, depending on the delivery rates of the fuel to be atomized,the following applies:

    0.2 mm≦(D.sup.i.sub.3 -D.sup.i.sub.2)≦6 mm,

    and typically (D.sup.i.sub.3 -D.sup.i.sub.2)=1 mm.

The purpose of each of the elementary atomizers is to eject a spray ofdroplets in a precise direction. This direction is the direction of theaxis of channel 224 and hollow elementary conduit C₃ for liquid fuel.

To ensure this precise orientation of the trajectories of the dropletscomposing the spray, it is necessary to have perfect coaxiality betweenthe axis of channel 224 and that of hollow elementary conduit C₃. Thusthe criterion is:

    α.sup.i.sub.1 =α.sup.i.sub.2.

Furthermore, the Length of the hollow elementary conduit and the lengthof its respective channel must be sufficient to secure establishment ofthe flows of the two fluids in their respective conduits. If one wishesthat the two fluids enter the combustion chamber with the sameorientation of the axial components of their respective velocityvectors, it is preferred that:

    L.sup.i.sub.1 ≧5 D.sup.i.sub.1 and typically L.sup.i.sub.1 =10 D.sup.i.sub.1

    L.sup.i.sub.2 ≧5 (D.sup.i.sub.3 -D.sup.i.sub.2) and typically L.sup.i.sub.2 =15 (D.sup.i.sub.3 -D.sup.i.sub.2)

D. Distribution of Fluids Among the Different Elementary Atomizers

To ensure a proper distribution of the liquid fuel among the differenthollow elementary conduits C composing the device, the criterion to besatisfied is:

    D.sub.OI.sup.2 ≧1.3Σ.sub.i D.sup.i.sub.1.sup.2 and typically D.sub.OI =4 mm.

Furthermore, the lengths of the different hollow elementary conduits Cmust be as close to one another as possible:

Letting i and j be two elementary atomizers, L^(i) ₁ =L^(j) ₁.

Depending on whether one does or does not wish to distribute differentliquid fuel delivery rates to each of the hollow elementary conduits C,one may or may not choose D^(i) ₁ values specific to each of the hollowelementary conduits C. The larger D^(i) ₁ is, the more fuel will becarried by hollow elementary atomizer i.

To ensure a proper distribution of atomizing fluid to the variouselementary atomizer channels 224 comprising the device, the criterion tobe satisfied is:

    D.sub.FI.sup.2 -D.sub.OE.sup.2 ≧1.3Σ.sub.i (D.sup.i.sub.3.sup.2 -D.sup.i.sub.2.sup.2).

Furthermore, the lengths of the different conduits must be as close toone another as possible:

Letting i and j be two elementary atomizers, L^(i) ₂ =L^(j) ₂.

E. Relative Angles Between Different Elementary Atomizers: Example of aDevice Having Three Elementary Atomizers (FIG. 18)

The relative angle between the different elementary atomizers is afunction of the number of elementary atomizers composing the atomizationdevice and the flame morphology one wishes to obtain. Thus:

    0°≦α.sup.i.sub.1 ≦60° and 0°≦α.sup.i.sub.2 ≦60°.

In general, the greater the number of elementary atomizers and thelarger the relative angles between these elementary atomizers, the widerand shorter the flame will be. Conversely, an atomization device havingtwo elementary atomizers with a low relative angle (on the order of 10°,that is α¹ ₁ =α¹ ₂ =5° and α² ₁ =α² ₂ =5°) will produce a long andstraight flame.

By way of example, the following flames were obtained in industrialtests in a glass furnace and in a pilot furnace with two atomizationdevices each having three elementary atomizers:

Fuel oil delivery rate=100 kg/h; atomizing air delivery rate=20 kg/h.

Device A (FIG. 18):

    α.sup.1.sub.1 =α.sup.1.sub.2 =16°; α.sup.2.sub.1 =α.sup.2.sub.2 =0°; α.sup.3.sub.1 =α.sup.3.sub.2 =16°.

    D.sup.1.sub.1 =D.sup.2.sub.1 =D.sup.3.sub.1 =2.0 mm.

Length of visible flame=3.5 m.

Width of visible flame=1.5 m.

Device B (FIG. 18):

    α.sup.1.sub.1 =α.sup.1.sub.2 =12°; α.sup.2.sub.1 =α.sup.2.sub.2 =0°; α.sup.3.sub.1 =α.sup.3.sub.2 =12°.

    D.sup.1.sub.1 =D.sup.2.sub.1 =D.sup.3.sub.1 =2.0 mm.

Length of visible flame=4.5 m.

Width of visible flame=0.7 m.

Depending on the respective angles for the elementary atomizers and therelative diameter of the hollow elementary conduits C carrying theliquid fuel, it is also possible to obtain separate flames for each ofthe elementary atomizers.

Thus, at the same fuel oil and atomizing air delivery rates, one has:

Device C (FIG. 18):

    α.sup.1.sub.1 =α.sup.1.sub.2 =20°; α.sup.2.sub.1 =α.sup.2.sub.2 =0°; α.sup.3.sub.1 =α.sup.3.sub.2 =20°.

    D.sup.1.sub.1 =D.sup.2.sub.1 =D.sup.3.sub.1 =2.0 mm.

Length of 3 separate visible flames=1.5 m.

Width of 3 separate visible flames=0.5 m.

F. Additional Characteristics of the Outer Nozzle Related to the Use ofthe Atomization Device in Glass Furnaces (FIGS. 19a and 19b)

In the case of continuous use of the inventive liquid fuel atomizer 200in glass furnaces (combustion chambers with elevated temperaturesranging from 1500° C. to 1670° C.) the liquid fuel atomizer of theinvention must be capable of ensuring production of a stable flame forperiods on the order of months. The atomization principle selected makesit possible to keep the temperature of the metal parts composing thedevice below 1100° C. Thus, the temperature measured at the tip of thedevice during an industrial test for one month in a glass furnace at1600° C. never exceeded 800° C.

These temperatures, which are not very high compared to the meltingtemperature of glass (˜1350° C.), give rise to a condensation phenomenonby the vitreous materials present in glass furnaces.

To avoid the formation of a layer of glass condensates on the outside ofouter nozzle 210, two symmetrical orifices 230, 232 are provided in theouter nozzle 210 (FIG. 19a and FIG. 19b) generally vertically aligned ina plane designated 240. The diameter D_(OR) and the elevation H_(OR) areestablished in such a way that the jet of atomizing fluid emerging fromthe orifices 230, 232 covers the entire surface of the exit end 208 ofthe outer nozzle 210.

Typically, D_(OR) ˜1 mm and H_(OR) ˜10 mm.

G. Control of the Flame Length at a Fixed Geometry

For a given geometry of the liquid fuel atomizer 200 of the presentinvention, it is possible to significantly vary the length of the flame(or flames) produced by a burner using this device. The flexibility (interms of flame length at constant fuel delivery rate) observed when theliquid fuel atomizer 200 is deployed in a glass furnace corresponds to aratio of one to three (flame length varying from about 3.7 to about 1.2m).

This control of the flame length is achieved by increasing or decreasingthe delivery rate of the atomizing fluid flowing between the outernozzle 210 and the hollow elementary conduits C. This variation indelivery rate is directly linked to the variation in pressure of theatomizing fluid upstream from the liquid fuel atomizer 200.

In ordinary use, the liquid fuel atomizer 200 functions at an atomizingfluid pressure between about 1 and 6 bars relative. The higher thepressure of the atomizing fluid, the higher also will be the deliveryrate of atomizing fluid and the shorter and "harder" the obtained flame(or flames) will be. This phenomenon is directly attributable to thechange in the particle size distribution of the droplets of liquid fuelcomposing the spray that is formed: the increase in the rate of deliveryof atomizing fluid has the effect of decreasing the average spraydroplet diameter and narrowing the distribution of the diameters aboutthis mean value. Conversely, a decrease in the rate of delivery ofatomizing fluid will increase the average diameter while widening thedistribution.

The overall mechanism of combustion of a liquid fuel reveals threecharacteristic times which, according to their respective weights,completely determine the type of flame resulting from a givenatomization. These three characteristic times are: the evaporation time,the chemical time, and the hydrodynamic time. Obtaining a particle sizedistribution confined narrowly about small drop diameters leads to adecreased time for vaporization of the droplets and thus an increasedrapidity of deflagration since the chemical time remains nearlyconstant. A spray characterized by such a distribution (high atomizingfluid delivery rate) will thus produce a short flame typical of a rapidcombustion and very localized in space.

Preferred pressurized atomization fluids are employed, such aspressurized air, steam, water vapor, and the like.

III. Other Burner Assembly Embodiments

FIG. 20a is a schematic illustration of a refractory block 5 and fuelgas cavity 94 in same, while FIG. 20b is a schematic illustrating acavity throat diameter D' and gas a exit diameter D for an injector orcavity. For fuel gas, the ratio of 1 (from FIG. 2, the distance betweenadjacent fuel gas exits) and D' (fuel cavity or injector throatdiameter) ranges from about 1.5 to about 10, more preferably from about1.5 to about 3, and most preferably about 2. FIG. 20a also illustratesthat the cavities in the refractory block may have varying diameter inthe direction of gas flow, and that the gas exits are generallycontoured at the exits, allowing the exits to be less likely to beplugged.

FIGS. 21 and 22 are gas exit end elevation views of two other refractoryblock embodiments within the invention, illustrating oxidant cavities91a and 91b. The embodiment of FIG. 21 illustrates that the fuel gascavities 94 may have concentric gas injectors in each cavity, wherebyfor example, fuel may injected in small diameter fuel gas injector 94'for low power operation, and through either the large diameter fuel gasinjector 94 only, or through both injectors 94 and 94' for high powerburner operation. Control of fuel flow between 94 and 94' may becontrolled by suitable valving arrangements, or through the use of anorifice in the line feeding one or the other of 94 and 94'. A liquidfuel injector 95 is also illustrated.

FIG. 22 illustrates a very important alternative refractory blockembodiment within the invention, wherein it has been discovered thatflame stability is significantly increased when the peripheral oxidantinjectors 91a and 91b, when positioned as illustrated, have a distanceseparating them of L, is greater than two times the distance l betweenadjacent fuel injectors, that is when L>21. This is true also when thefuel and oxidant are injected via the use only of injectors, rather thanthe use of a refractory block.

FIGS. 23-31 illustrate, in front elevation views, other embodiments ofburner assemblies of the invention. FIG. 23 illustrates an embodimentwherein the two oxidant cavities 91a and 91b have exits which arerectangular, also illustrating three fuel gas exits 94 and a liquid fuelexit 95.

FIG. 24 illustrates an embodiment wherein oxidant emanates from twooxidant exits 91a and 91b, and oxidant also emanates from three annularportions 91' which surround respectively three fuel exits 94'.

FIG. 25 illustrates an embodiment wherein a single oxidant exit 91 ispresent as a rectangle having a width much greater than its height. Inthis embodiment, the ratio of width to height of the oxidant cavity exitmay range from 1:1 up to about 4:1.

FIG. 26 illustrates an embodiment wherein the two oxidant cavities 91aand 91b have exits which are ellipsoid, also illustrating three fuel gasexits 94.

FIG. 27 illustrates an embodiment similar to the embodiment of FIG. 26,with the addition of a liquid fuel cavity 95 having a circular exit.

FIG. 28 illustrates an embodiment wherein a single ellipsoid oxidantexit 91 is present with three fuel gas cavities 94 having circularexits.

FIG. 29 illustrates an embodiment similar to the embodiment of FIG. 28,with the addition of a liquid fuel cavity 95 having a circular exit.

FIG. 30 illustrates an embodiment wherein a single ellipsoid oxidantexit 91 is present with two fuel gas cavities 94 having circular exits.

FIG. 31 illustrates an embodiment similar to the embodiment of FIG. 30wherein a single ellipsoid oxidant exit 91 is present with two fuel gascavities 94 having circular exits, with the addition of a liquid fuelcavity 95 having a circular exit.

FIGS. 32 and 33 illustrate embodiments wherein oxidant emanates from oneor more positions both above and below the fuel exit(s). In theseembodiments, the fuel cavities are essentially parallel to the loweroxidant cavities, while the upper oxidant cavities are angled down sothat the upper oxidant fluid flow converges with the fuel fluid flow andthe lower oxidant fluid flows in the combustion chamber. Thus, in FIG.32, duel oxidant exits 91a and 91b are positioned above and below,respectively, of a single fuel exit 94. FIG. 33 illustrates a similarembodiment, except that there are two oxidant exits 91a and 91b abovetwo fuel exits 94, and two oxidant exits 91a' and 91b' below the duelfuel exits. More than two fuel exits, with corresponding upper and loweroxidant exits, can be envisioned.

Many other embodiments are possible and can easily be envisioned by theskilled artisan after having read and understood the above.

It is important to point out that the exits of oxidant and fuel in allembodiments are preferably contoured, as depicted for example in FIGS.8-11.

Having described the present invention, it will be readily apparent tothe artisan that many changes and modifications may be made to theabove-described embodiments without departing from the spirit and thescope of the present invention.

What is claimed is:
 1. A method of controlling flame length using aliquid fuel atomizer comprising a first hollow cylinder, the firsthollow cylinder having a fuel exit end with a single fuel exit fluidlycommunicating with a plurality of hollow elementary conduits, and anouter nozzle formed from a second hollow cylinder extended by a profiledpart comprised of two symmetrical cowls and having a fuel exit end andhaving a plurality of fuel exits, the outer nozzle having an internaldiameter greater than an external diameter of the first hollow cylinder,the second hollow cylinder completely surrounding the single fuel exitof the first hollow cylinder, the profiled part having an interior whichis pierced by a plurality of channels, the plurality of channels beingequivalent in number to the plurality of hollow elementary conduits, thechannels merging with an interior of the second hollow cylinder andterminating at the fuel exit end of the second hollow cylinder, to forma space for flow of atomizing fluid surrounding the hollow elementaryconduits, the first hollow cylinder having an axis, the methodcomprising increasing or decreasing a delivery rate of the atomizingfluid.
 2. Method in accordance with claim 1 wherein the control of flamelength occurs using an atomizing fluid pressure ranging from about 1 toabout 6 bars relative.
 3. Method in accordance with claim 1 wherein theatomization fluid is selected from the group consisting of pressurizedair, steam, water vapor, and combinations thereof.
 4. A burner assemblyhaving improved flame length and shape control, the burner assemblycomprising a refractory block adapted to be in fluid connection withsources of oxidant and fuel, the refractory block having a fuel andoxidant entrance end and a fuel and oxidant exit end, the exit endhaving fuel exits and oxidants exits, the refractory block furtherhaving a plurality of fuel cavities, at least two of the fuel cavitiesdefining a first fuel plane, and a plurality of oxidant cavitiesdefining a second oxidant plane, the fuel cavities being more numerousthan the oxidant cavities, at least one of the fuel cavities havingpositioned therein a liquid fuel atomizer comprising a first hollowcylinder, the first hollow cylinder having a fuel exit end with a singlefuel exit fluidly communicating with a plurality of hollow elementaryconduits, and an outer nozzle formed from a second hollow cylinderextended by a profiled part comprised of two symmetrical cowls andhaving a fuel exit end and having a plurality of fuel exits, the outernozzle having an internal diameter greater than an external diameter ofthe first hollow cylinder, the second hollow cylinder completelysurrounding the single fuel exit of the first hollow cylinder, theprofiled part having an interior which is pierced by a plurality ofchannels, the plurality of channels being equivalent in number to theplurality of hollow elementary conduits, the channels merging with aninterior of the second hollow cylinder and terminating at the fuel exitend of the second hollow cylinder, to form a space for flow of atomizingfluid surrounding the hollow elementary conduits, the first hollowcylinder having an axis.
 5. A liquid fuel atomizer comprisinga firsthollow cylinder, the first hollow cylinder having a fuel exit end with asingle fuel exit fluidly communicating with a plurality of hollowelementary conduits; and an outer nozzle formed from a second hollowcylinder extended by a profiled part comprised of two symmetrical cowlsand having a fuel exit end and having a plurality of fuel exits, theouter nozzle having an internal diameter greater than an externaldiameter of the first hollow cylinder, the second hollow cylindercompletely surrounding the single fuel exit of the first hollowcylinder, the profiled part having an interior which is pierced by aplurality of channels, the plurality of channels being equivalent innumber to the plurality of hollow elementary conduits, the channelsmerging with an interior of the second hollow cylinder and terminatingat the fuel exit end of the second hollow cylinder, to form a space forflow of atomizing fluid surrounding the hollow elementary conduits, thefirst hollow cylinder having an axis.
 6. Device in accordance with claim5 wherein the number of hollow elementary conduits ranges from 2 to 5.7. Device in accordance with claim 6 wherein an axis of all of thehollow elementary conduits are in the same plane, denoted as the sprayplane.
 8. Device in accordance with claim 7 wherein each hollowelementary conduit has an inside diameter and an outside diameterwherein the inside diameter is greater than or equal to 0.5 mm, and theoutside diameter exceeds the inside diameter by less than or equal to 6mm.
 9. Device in accordance with claim 8 wherein each hollow elementaryconduit has an inclination angle with respect to the axis of the firsthollow cylinder.
 10. Device in accordance with claim 9 wherein eachchannel has an inclination angle with respect to the axis of the firsthollow cylinder, the angle being in the spray plane.
 11. Device inaccordance with claim 10 wherein the axis of the first hollow cylinderis concentric with an axis of the second hollow cylinder.
 12. Device inaccordance with claim 10 wherein the inclination angle of each hollowelementary conduit is equivalent to the inclination angle of itscorresponding respective channel.
 13. Device in accordance with claim 12wherein each inclination angle ranges from 0° to 60°.
 14. Device inaccordance with claim 7 wherein the profiled part has two cleansingorifices fluidly communicating with the interior of the second hollowcylinder, each orifice positioned away from the spray plane in such away that a jet of atomizing fluid emerges from each of the cleansingorifices at an exterior of the outer nozzle.
 15. The device of claim 5wherein each channel has a shape which is substantially the same as thatof its corresponding hollow elementary conduit.
 16. Device in accordancewith claim 5 wherein the space between each hollow elementary conduitand its respective channel is proportioned in such a way that a velocityof the atomizing fluid in said channel follows the relationship:

    Mach 0.3≦V.sub.atomizing fluid ≦Mach 1.2.


17. Device in accordance with claim 5 wherein each hollow elementaryconduit has a length greater than or equal to five times an internaldiameter of the hollow elementary conduit.
 18. Device in accordance withclaim 17 wherein each channel has a length which is greater than orequal to five times the difference between a diameter of the channel andan external diameter of its corresponding hollow elementary conduit. 19.Device in accordance with claim 18 wherein each channel has a lengthwhich is greater than or equal to fifteen times the difference between adiameter of the channel and an external diameter of its correspondinghollow elementary conduit.
 20. Device in accordance with claim 19wherein a diameter of the first hollow cylinder, when squared, isgreater than or equal to 1.3 times a sum of squares of internaldiameters of all hollow elementary conduits.
 21. Device in accordancewith claim 20 wherein lengths of all hollow elementary conduits are allequal.
 22. Device in accordance with claim 21 wherein the difference ofsquares between inside diameter of the second hollow conduit and outsidediameter of first hollow conduit is greater than or equal to 1.3 timesthe sum of the differences of squares of the diameter of a channel andan outside diameter of its corresponding hollow elementary conduit.